1. Field of Invention
The present invention relates to a fan and a motor thereof and, in particular, to a fan and an inner rotor motor thereof.
2. Related Art
Nowadays, electronic products are minimized and have powerful functions, so that the demands for heat dissipation are increased accordingly. That is, the heat dissipation efficiency must be increased for the electronic products. Because the fan has the advantages of low cost and well developed, it is widely used as a heat dissipating device.
Referring to FIG. 1, a conventional fan 1 has an impeller 11, a motor 12 and a frame 13. The motor 12 has a rotor magnet 121 and a stator 122. The rotor magnet 121 is disposed on the inner surface of the hub 111 of the impeller 11, and the rotor magnet 121 is located around outside of the stator 122 corresponding to the stator 122.
However, when the rotor magnet 121 is disposed around the outside of the stator 122, the rotation radius, which is the distance between the rotor magnet 121 and the axis 123, is long. Thus, the rotational inertia of the rotor magnetic 121 is large. Therefore, the conventional fan 1 requires higher initializing voltage and needs more time to reach the rated speed.
Also, the large rotational inertia of the rotor magnet 121 causes the poor response speed of the fan 1 in different duty cycles, so that the rotation speed of the fan 1 changes slowly. Moreover, when the fan 1 rotates in high speed, a significant vibration will occur. Furthermore, since the hub 111 of the impeller 11 is configured to cover the rotor magnet 121 and the stator 122, it definitely has sufficient dimension, which causes the decreased area of the airflow channel so as to decreasing the air flux of the fan 1.